Circle of the Shepherd Druid Guide to Fuzzy Fury

[Nidgit]

As a druid, I would hope this interpretation isn't true, because incapacitation causes you to lose concentration, and if you automatically lose concentration whenever you're knocked out of Wild Shape, that is bad news.

I don't think it is true though. At no time are you actually at 0 HP and therefore incapacitated; instead you just turn back into a human(oid).

There's nothing that says you lose concentration when you hit 0 HP, though, and Faithful Summons doesn't require you to be incapacitated either. Normally reaching 0 HP causes Unconciousness, which then causes Incapacitation, which breaks concentration. Wild Shape specifies that you don't go Unconscious unless the damage you take pushes you to 0 HP in your humanoid form, but does say you revert when you drop to 0 HP while Wild Shaped. So you should hit still hit 0 HP when knocked out of Wild Shape to activate Faithful Summons, but you're never Unconscious or Incapacitated to break Concentration. You just have to make the saving throw as normal.